There are numerous approaches to producing electricity from the hydraulic force of the localized movement of water in large bodies of water. Water moving as a result of tides, winds, or gravity, for example, has been used as a hydraulic force to move some turbine, door, or other part of a larger apparatus anchored to land. This approach is expensive, not very efficient, and prone to breaking down both because of the difficulty in anchoring the apparatus to land and because the ocean is corrosive and small sand particles in the ocean cause excessive wear.
The power density of wind and water, two abundant natural resources, is very low. It is not until wind is blowing in excess of 100 MPH that it will, blow a standing person over, and if a person is floating in even large ocean waves the force of the waves flows by you because water is a low-density liquid. One can feel the energy of the wave, but the force is minimal as compared to standing in the road and being hit by a bus traveling at the same speed as the wind or water. Force equals the density of an object multiplied by the speed that it is traveling, so very low-density substances like wind and water do not make very good energy resources because the scale of energy projects for wind and water have to be extremely large and expensive and can also have extensive environmental impact on our planet, such as large hydro projects.
The solution to creating bountiful, renewable, non-carbon producing, cheap energy for our planet is to figure out a way to generate high power density energy like that of a coal fired or nuclear power plant using low-density wind and/or water, the most plentiful resources on our planet.
Unfortunately, prior attempts to produce electrical power from waves have failed to appreciate the various degrees of freedom involved and therefore have been inefficient. Furthermore, some systems have been unstable with components diverging even, in relatively calm sea states.